Need to rig a rack on a compact frame.
 

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If you don't have braze ons near the seat post, then you can try to rig it to the seat stays with p-clamps. Are you using the rack to accomodate pannier(s)? If so, you might have heal strike issues with the small frame. I have a compact frame and got this rack so I could get the pannier back far enough for heal clearance. http://www.oldmanmountain.com/red_gallery.htm

The bike I have this on has caliper brakes, so no v-brake/canti posts to attach to like in the picture. I ordered rubber coated p-clamps and attached it to the seat stays instead.

The seat post clamp's bolt has served very well (for rack mounting) on a bike of mine, but it depends on the exact situation.

On some bikes it might make sense to attach another (second) clamp higher up, directly onto the seat post itself.

Is the seatpost carbon? I don't know how much pressure a CF seatpost will be able to take from a clamp. Probably mot much. If it isn't carbon, you could probably pretty easily rig something up, or if you're not carrying much, get a seatpost mounted rack.

Might consider a saddle bag... Carradice, Rivendell, etc, although usually a rack+panniers can carry heavier loads.

I have a Schwinn Mesa GSD that I rigged for commuting duty until I got my touring bike. It worked ok. I rigged a Topeak disk brake rack to it. The bottom part bolts on normally, but the top was difficult. What I did was take some perforated metal strapping from a home improvement store and rigged it up with that. It worked great. Wish I had a picture of it.

Check this site out.

Wow, that's the way to do it. My way is gheto.